The present invention relates to the field of audio-visual signal transmission and reception. More particularly, the present invention relates to a method and apparatus for scrambling an audio-visual signal during transmission in order to control reception and use of the signal.
Cable and pay-per-view television programming are extremely popular and widely available around the globe in modern society. Those firms providing such programming are frequently lucrative and successful. This success comes, in part, from the ability to prevent those who have not purchased the service from receiving and using the television signals transmitted by the service provider.
In general, it is common for a cable company or other service provider to scramble its signals to prevent their use by unauthorized parties. This scrambling is intended to make the signals unintelligible to typical television sets which are not authorized to receive and use the scrambled signal. When the signal is scrambled, a conventional television will not recognize the signal, or at best, display only a distorted image from the signal.
Cable companies which provide a number of channels over a cable connection may only scramble certain channels so that cable subscribers can be required to pay additional fees for receiving these xe2x80x9cpremiumxe2x80x9d channels. The premium channels are typically movie or adult channels.
Those subscribers who have paid the service provider for reception of the scrambled signal will be given equipment for use with their television sets which unscrambles the signal. With this equipment, the authorized user can unscramble and receive the service provider""s signals and view the programming contained in the transmission.
A well-known conventional method of scrambling a signal to prevent its unauthorized reception is to reverse the spectral positions of the audio and video portions of the signal. Typically, an audio-visual signal will have an audio carrier signal at a first frequency and a video carrier signal at a second frequency. The carrier signals are modulated to carry the respective video and audio data of the transmitted programming.
If, however, the audio carrier signal is transmitted at the second (video carrier) frequency, and the video carrier signal is transmitted at the first (audio carrier) frequency, the signal is scrambled. A television tuner will be attempting to receive the audio signal at the first frequency and the video signal at the second frequency, and will be unable to receive the reversed signal properly.
Many other methods of scrambling audio-visual signals during transmission are known in the art. However, all are subject to various deficiencies. For example, many scrambling methods are only partially effective. Thus, while the scrambled signal is not received clearly, the image and audio may still be intelligible.
Accordingly, there is a need in the art for an improved and more effective means and method of scrambling an audio-visual signal.
It is an object of the present invention to meet the above-described needs and others. Specifically, it is an object of the present invention to provide a method and apparatus for scrambling an audio-visual signal and for receiving and unscrambling the scrambled signal that is highly effective.
Additional objects, advantages and novel features of the invention will be set forth in the description which follows or may be learned by those skilled in the art through reading these materials or practicing the invention. The objects and advantages of the invention may be achieved through the means recited in the attached claims.
To achieve these stated and other objects, the present invention may be embodied as a method of controlling access to a broadcast video signal by scrambling the video signal by modifying at least one of the horizontal or vertical sync component of the video signal so as to render the signal unstable when received by a conventional television set.
Preferably, the method of the present invention includes modifying the vertical sync component of the video signal by removing the vertical sync component from the video signal entirely. This replacement is illustrated in FIG. 3. Following removal of the vertical sync component, the method of the present invention includes inserting the horizontal sync component in the video signal in place of the removed vertical sync component. A final step in the scrambling process is the insertion of the vertical blanking interval (VBI) scramble mode data. The scrambled signal may then be broadcast.
The method of the present invention also encompasses the process of unscrambling the scrambled video signal by receiving the video signal with the modified vertical sync component; synchronizing to and receiving VBI scramble mode data; and reconstructing the vertical sync component. The method concludes by inserting the recreated vertical sync component into the received video signal so that the received video signal may be properly displayed by a television set.
The present invention also encompasses a scrambler for scrambling a video signal under the principles of the present invention. The scrambler of the present invention includes: an input terminal for receiving a video signal; and a signal conditioner which receives the video signal from the input terminal and removes therefrom the vertical sync component of the video signal.
The scrambler of the present invention further includes a sync processor that first extracts the horizontal and vertical sync component for synchronization to incoming video and then inserts horizontal sync components in the VBI. A multiplexer receives an output signal from the signal conditioner, the horizontal sync component from the sync processor, and scramble mode data from the data inserter. The multiplexer then inserts the horizontal sync component in the video signal in place of the extracted vertical sync component. A control logic circuit controls the operation of the multiplexer, the sync processor and the data inserter.
Finally, the scrambler of the present invention preferably includes an amplifier for receiving the scrambled video signal from the multiplexer and outputting the scrambled video signal through an output terminal.
Finally, the present invention also encompasses a descrambler for unscrambling a scrambled video signal which has been scrambled according to the principles of the present invention by inserting a horizontal sync signal component in place of the vertical sync signal component. The descrambler of the present invention includes: an input terminal for receiving the scrambled video signal; a scramble mode data receiver that is used to lock to the scramble mode data in the incoming video signal; a control logic circuit for controlling the timing and multiplexing in the descrambler; a vertical sync generator controlled by the control logic circuit for generating the vertical sync component based on the output of the signal processor as provided to the control logic circuit; and a multiplexer, controlled by the control logic circuit, for receiving the scrambled video signal from the input terminal, receiving the vertical sync component from the vertical sync generator, and inserting the vertical sync component into the scrambled video signal so as to produce an descrambled video signal.
Preferably, the descrambler of the present invention also includes an output terminal for receiving the unscrambled video signal from the multiplexer and providing the unscrambled video signal to a television set. The unscrambled video signal can then be properly displayed on a conventional television set with the television able to stabilize the picture vertically and horizontally.